Development and Evaluation of Extracorporeal Gas Exchangers for Multi-Function Use in Respiratory Failure.

Abstract

In the U.S., there are 400,000 respiratory failure deaths. Conventional treatment for acute respiratory failure employs lung damaging mechanical ventilation. The only long term treatment for chronic respiratory failure is lung transplantation. However, only 1800 transplants are performed each year due to donor shortages, resulting in the need for a destination therapy. Extracorporeal gas exchangers have been used as an alternative to mechanical ventilation in acute respiratory failure and as a bridge to transplantation in chronic respiratory failure. Blood is diverted to an extracorporeal gas exchanger, where oxygen is added and carbon dioxide is removed before returning the blood to the patient. Current gas exchangers are limited by their high resistance and low biocompatibility that lead to patient complications and device clot formation. This dissertation discusses three gas exchangers; the compliant thoracic artificial lung (cTAL), the compact cardiopulmonary support device (CCSD), and the pulmonary assist device (PAD).

Fourteen day in vivo studies evaluated the cTAL’s long term performance and biocompatibility. The uncoated cTAL was capable of 14 days of support without a resistance increase or clot formation. In the future, the cTAL will be coated with anti-coagulant coatings and tested in vivo for 2 months. Individual components of the CCSD were designed and when tested, met design goals. However, enclosure pressures of negative 197 mmHg at flowrates of 4 L/min were encountered in CCSD system testing, causing gas embolus formation. The risk of gas embolus resulted in the discontinuation of CCSD development. The PAD was designed for long term use as a bridge to transplantation and destination therapy. Computational simulations were used to design the PAD with a theoretical resistance of 1.50 mmHg/(L/min) and a 98.3 percent blood outlet oxyhemoglobin saturation at blood flowrates of 1.25 L/min. In vitro testing of the PAD yielded lower gas exchange performance (88.4 percent saturation) and higher resistance (3.47 mmHg/(L/min)). However, the gas exchange performance was skewed negatively by two devices with fabrication defects. PADs without defects were closer to the gas exchange goal. Future computational models will be improved, and the PAD will be redesigned for lower resistance and higher gas exchange.